The euro zone may need to spend only 10 billion euros or less to help recapitalize Greek banks, a senior EU official said, after an ECB test showed the sector would need an extra 14.4 billion euros of capital if major risks materialized.

Euro zone creditors have earmarked up to 25 billion euros ($27 billion) within the latest, 86-billion-euro bailout, to recapitalize banks after people pulled their money out earlier this year fearing Greece might leave the euro zone.

"It looks like ... out of the envelope of the 25 billion ... the 10 billion which is sitting in the ESM (European Stability Mechanism) would suffice," a senior EU official said.

"Given the results of the comprehensive assessment (of bank capital needs by the European Central Bank) I don't think anybody will be obsessing about this ... until the 15th of November, because as it turns out, the 10 billion will suffice for now."

The release of the remaining 15 billion, now unlikely to be needed, is linked to the completion of a formal stage in the bailout called the first review, in which creditors assess which of the agreed reforms have been implemented.

Euro zone finance ministers will discuss progress in the implementation of Greek reforms next Monday.

The outstanding issues on which Athens and the creditors still need to find agreement are a law on foreclosures, value-added tax (VAT) on private schools, VAT and social security payments for debtors and minimum prices of generic drugs.

Euro zone ministers agreed this first review should be finished no later than Nov. 15. Many officials now see this as unrealistic because of some delays in the process, so if Greece had needed to use the remaining 15 billion euros, it may well have been unable to do so.

More money to boost Greek bank capital is likely to come from private investors, keen not to dilute their current holdings too much, as well as from losses imposed on existing shareholders and junior bondholders of Greek banks.

While an EU law that imposes losses on senior bondholders of banks comes into force only on Jan. 1, euro zone finance ministers agreed in August that senior bondholders of Greek banks would also have to contribute to the recapitalization.

"There needs to be, under most circumstances, a contribution from senior bondholders," the official said, but said its size depended on several other factors along the recapitalization process.